London — Britain prided itself on ruling the waves in the 19th century; they might once again in the 21st century. But not with its Navy. This time, Britain's chosen vessels are new technologies that convert the pounding of the waves and the ebbing of tides into the thrum of electricity.

While still years behind other alternative-energy forms, wave and tidal power systems are already in the pipeline in Britain. Officials here stress that Britain aims to become a world leader in the new form of energy.

A range of multimillion-pound projects have been announced in recent weeks, promising to generate enough electricity for thousands of homes.

In addition, the government has ordered a feasibility study into a $30 billion, 10-mile hydroelectric barrage across the Severn estuary in western England, which could provide almost 5 percent of the country's energy needs.

Sea power is an obvious solution for Britain. Its exposure to gusty Atlantic winds mean that wave patterns are ripe for power generation. Its craggy 7,000-mile coastline, comprising hundreds of islets, makes for fast-moving tidal currents that offer substantial hydroelectric possibilities.

"We have about the best resource in the world for both wave and tidal," says Gordon Edge of the British Wind Energy Association, the trade and professional body for Britain's wind and marine renewables industries. "Any country with a west coast does well for wave power because prevailing winds tend to come from the west." Even better, he adds, if you have a large ocean out to the west, across which prevailing winds can whip up large waves.

Private sector leads the way

A Scottish company, Pelamis Wave Power, has spearheaded private-sector efforts to develop technology that can be towed out to sea and convert wave motion into energy.

Its large, red "sea snakes" are to be deployed in two "wave farms" in Britain - a 3 megawatt system off the Orkney Islands in Scotland and a second one off Cornwall in southwest England. The "snakes" are also ready to be towed to a site off the coast of Portugal.

The Orkney islands also host a marine energy think tank and testing site, the European Marine Energy Centre. "There is enormous potential," says Jennifer Norris, the center's research manager. "Wave and tidal systems have a big place in the future" of power generation in Britain.

On tidal systems, meanwhile, the European power company E.ON is developing a facility off western England that will produce enough energy to power 5,000 homes.

Overall, wave and tidal systems have the potential to deliver up to 20 percent of Britain's electricity needs, experts say – a tempting opportunity in a country that is struggling to meet EU targets for sourcing one-fifth of energy supply from renewables by 2020, and will probably fail to attain its own goal to cut CO2 emissions by 20 percent over the 1990-2010 period.

But there are telling challenges to sea power, principally involving cost and environmental threats.

Concerns over coastal habitat

Last week, the government was warned by its own task force, the Sustainable Development Commission, that if it wanted to build the Severn tidal system it would have to address major concerns over loss of estuary habitats for rare species.

"The enormous potential for a Severn barrage to help reduce our carbon emissions and improve energy security needs to be balanced against the impact on the estuary's unique habitat," said commission chairman Jonathan Porritt, adding that the government, not the private sector, would have to take charge to assure "a sustainable long-term approach."

Even if it finds an environmentally acceptable solution, the formidable cost of the barrage will produce electricity three times more expensive per kWh than gas.

Cost is a major hurdle for wave power developers, too. Early systems suggest a cost of as much as 25 cents per kWh, expensive even in a world of rising hydrocarbon prices.

But developers are sanguine. New technology is always pricey, and costs will fall if enough power suppliers order the systems. They have already started: in Britain, power suppliers are compelled by a government-imposed "renewables obligation" to source a growing proportion of energy from renewables. To give marine energy a leg up, it will count double.

"There has never been a new technology that has been economic out of the box," says Max Carcas, business development director at Pelamis Wave Power. "If you look at coal-fired generation in the UK in the 1920s, it was 50 cents per kWh. Over time that came down." So, he adds, did the cost of wind turbines, which have fallen 80 percent over the past 25 years.

In any case, he argues, better to invest now than be sorry in 50 years. "It's a global concern to bring on new energy technology that will displace CO2-emitting technology," Carcas says.

Pontes adds that if the environmental cost of hydrocarbons are factored in, gas and oil-based power generation doesn't look so cheap anymore. "If you have a carbon tax, then there would be similar costs for conventional energy sources" as for renewable energy, she says.